The present invention is directed generally to templates used in the creation of thin-film replicas, for example, the creation of thin films, such as carbon films, for use as specimen support in electron-beam specimen analysis. More specifically, the present invention is directed to novel reusable templates, the methodology of making these reusable templates, the templates made from such methodologies, the use and reuse of these templates to make thin films of any type for any purpose, and the thin films made from these templates.
Several issued U.S. patents provide a background for structures and methods of making replicas. For example, U.S. Pat. No. 2,347,965 to Ramberg discloses a method to make a replica of the surface of an opaque specimen through a two-step positive replication process for examination with a transmission electron microscope. In the disclosed process a specimen is first coated with a thick amount of metal. The thick metal coating is mechanically stripped from the specimen and coated with a thin replicating material. The replica is completed by chemically dissolving the metal to leave only the thin replicating material. Thus, the negative metal replica of the specimen surface is destroyed and can be used to create only one positive replica.
U.S. Pat. No. 2,572,497 to Law discloses a method to make a positive silica replica of a copper mesh. In this patent, a copper mesh serves as a template for creating a silica mesh. As the process is described, the silica mesh is completed by etching away the underlying copper mesh. The copper mesh template is destroyed in the manufacture of the silica replica and can therefore only be used one time.
U.S. Pat. No. 2,875,341 to Nesh discloses a method for making a replica of a metallic surface through a two-step positive replication process. The process disclosed in the patent requires that a metallic object to be replicated have the shape of the inner edge of a ring or can be cut to have said shape. In the first step of the replication process, a plastic replica of the metallic surface is made whereby plastic is applied to the metallic surface, and as the plastic dries, it shrinks and separates itself from the metallic surface. The plastic mold of the surface is then evaporated with silica and possibly other masking materials. Finally, the plastic is dissolved from the silica replica with solvents. Accordingly each plastic mold from the surface can be used to create only one replica.
U.S. Pat. No. 4,250,127 to Warren, et al., discloses a method to make a specimen support grid for x-ray analysis as a negative replica from a mold etched into a surface. The grid disclosed in this patent is created by casting a carbon material into a mold and etching away the mold once the casting is completed. Thus the mold (or template) disclosed in this patent is destroyed as a consequence of the process for making the grid.
U.S. Pat. No. 5,004,920 to Lee, et al., discloses a method to collect asbestos from a sample of air. In the disclosed process, a volume of air containing an asbestos sample to be collected is passed through a filter. The filter with the collected sample is affixed to a glass slide, coated with carbon both to form a negative replica of the surface and to trap the asbestos specimen, and then cut into small sections. The negative replica is completed by submersing a small section in solvent to dissolve the filter and thereby release the replica with embedded asbestos.
U.S. Pat. No. 6,645,744 to Ermantraut, et al., discloses a bath used to selectively etch layers of a microstructure wherein the bath consists of at least one biogenic agent. U.S. Pat. No. 6,821,692 also to Ermantraut, et al., discloses a method to create a self-supported novolac (i.e. photoresist) structure by the process of depositing, patterning, and releasing the structure from a substrate. See also, Ermantraut, E; Wolfhart, K; and Tichelaar, W, “Perforated support foils with pre-defined hole size, shape and arrangement,” Ultramicroscopy 74 (1998), pp 75-81 describing the usage of the technology described in these two patent references. Perforated support foils with holes of pre-defined size, shape and arrangement and with hole sizes down to the sub-micrometer range, named Quantifoil®, are presented. The foils are fabricated using semiconductor lithographic techniques. A sacrificial layer that consists of a biopolymer, i.e. glutaraldehyde cross-linked gelatin, is used. This layer is removed by proteinase treatment, thus introducing an enzymatic reaction as a tool in microsystems technology. The foils are particularly beneficial in electron microscopy, when a specimen support is required with holes smaller than those attainable with metal grids (˜10 μm). Foils with a specific hole size and arrangement permit a further automation of electron microscopic (EM) data acquisition procedures.
Additionally, Downing, K, “Support Films with Uniform Hole Size,” Microscopy Today, 11(5), p. 54, 2003 describes a method for producing a uniform distribution of holes that are all of the same size in holey carbon films mounted on standard EM grids used as specimen supports in electron cryo-microscopy. The resulting grids are described as being a very effective intermediate between holey films made with the various solvent techniques, which produce random hole sizes, and commercial Quantifoil® grids, which have uniform holes on a regular lattice.
However, the current state-of-the-art does not provide a template structure that allows for a positive replica to be created in a single step while preserving the template for reuse (i.e., the template is not sacrificed, destroyed or otherwise damaged during the removal of the replica). Moreover the prior art templates do not allow for precise control over the thickness and type of material used to form the replica. Nor can the prior art templates can be custom created to have features for replication down to the nanometer scale where the features can be precisely manufactured and transferred into the replica as a pattern of any complexity. Further, the there exists a need for the formation of thin film replicas from a template that can be accomplished on a large scale not requiring the template to but cut into small sections.